Buy a spark checker, see what you are getting on each plug. Do you get any misfire codes?

Still need to check fuel pressure though.

 

Checked fuel pressure today.

The first prime with cold engine went to 6 and back to 0. With engine turning over the gauge slowly crept up to 25 and the engine began sputtering on as usual. It quickly settled at 41 and ran steadily with a slightly rough idle as usual. I ran it for a few mins and it stayed at 41.

I shut it down for a minute and primed it again. This time it primed to 25 and back to 0. It started within 3 revolutions and fired off quickly with no sputtering. Slightly rough idle remains. Gauge went right back to 41.

Next I let it sit for 30 mins. It was enough time for it to cool down substantially. The gauge numbers and starting situation were the same as the initial cold start.

Conclusion: 6 psi of cold start prime doesn't provide enough fuel to quickly start the engine. 25 psi of warm start prime does provide enough fuel for a quicker start.

Is it possible there is an air leak up top allowing fuel to flow back into the tank when it sits? I would assume a 2-3 second prime wouldn't be enough time to properly fill an empty fuel line and rails. Any ideas? Thanks guys!

 

I wanna see how this turn's out, having sorta the same issue with a van, fuel pressure test and new filter coming this weekend.....

 

HeyYou is closer than I am on this... It may very well be bad pump or fuel filter problem which is internal to the pressure regulator which is mounted on the pump. A leak would be detected visually and nasally. if you have a leak then that is the problem...You should have well over 35 psi prime pressure at the gauge before cranking, manual says 2-3 seconds. There isn't a return for these systems so there is pressure at all times in the line, you have to relieve the pressure before removal of the tank. Try to prime the system for say 10 seconds...then turn the key off and go to the pressure relief valve with a towel or small plastic cup...you should get fuel spurting out. Prime the system again without cranking then wait like 10 minutes. If there is no fuel spurting at the relief valve; then there is a leak. If not then the pump/regulator must be the issue. Check the whole line to make sure...

*edit:
After reading your post again; if the pressure crept up from 6 to 25; that would seem to indicate a pump or regulator on the way out.

 

Thanks for the info, Brian. Yes, the prime pressure was 6 when cold and 25 when warm. Then back to 6 after cool down. I will check for a leak tomorrow and report back.

 

Your fuel pump is toast. You should get 49 pounds pressure..... and very close to that on the initial prime. Low pressure would also go a long ways toward explaining your rough idle.

 

I was wondering about that. Someone posted it should be 35 psi, and not being familiar with the V10 I did not say anything.

 

That was me. The manual states between 35 and 45 psi...6 is right out!

 

No fuel pressure at test port. Maybe the regulator is allowing fuel to flow back into the tank? Not sure. I don't see any fuel leaks on top or underneath. Any ideas? Or should I just replace the fuel pump? Thanks!

 

I would replace the pump. It obviously has some issues. Get the whole unit though, that will get you a new filter/regulator as well......